blog/data/2013-11-02-debian-init-d-script.txt

   1 Title: Debian init.d boot script example for rsyslog
   2 Tags: english, debian, bootsystem
   3 Date: 2013-11-02 22:40
   4
   5 <p>If one of the points of switching to a new init system in Debian is
   6 <a href="http://thomas.goirand.fr/blog/?p=147">to get rid of huge
   7 init.d scripts</a>, I doubt we need to switch away from sysvinit and
   8 init.d scripts at all.  Here is an example init.d script, ie a rewrite
   9 of /etc/init.d/rsyslog:</p>
  10
  11 <p><pre>
  12 #!/lib/init/init-d-script
  13 ### BEGIN INIT INFO
  14 # Provides:          rsyslog
  15 # Required-Start:    $remote_fs $time
  16 # Required-Stop:     umountnfs $time
  17 # X-Stop-After:      sendsigs
  18 # Default-Start:     2 3 4 5
  19 # Default-Stop:      0 1 6
  20 # Short-Description: enhanced syslogd
  21 # Description:       Rsyslog is an enhanced multi-threaded syslogd.
  22 #                    It is quite compatible to stock sysklogd and can be
  23 #                    used as a drop-in replacement.
  24 ### END INIT INFO
  25 DESC="enhanced syslogd"
  26 DAEMON=/usr/sbin/rsyslogd
  27 </pre></p>
  28
  29 <p>Pretty minimalistic to me... For the record, the original sysv-rc
  30 script was 137 lines, and the above is just 15 lines, most of it meta
  31 info/comments.</p>
  32
  33 <p>How to do this, you ask?  Well, one create a new script
  34 /lib/init/init-d-script looking something like this:
  35
  36 <p><pre>
  37 #!/bin/sh
  38
  39 # Define LSB log_* functions.
  40 # Depend on lsb-base (>= 3.2-14) to ensure that this file is present
  41 # and status_of_proc is working.
  42 . /lib/lsb/init-functions
  43
  44 #
  45 # Function that starts the daemon/service
  46
  47 #
  48 do_start()
  49 {
  50         # Return
  51         #   0 if daemon has been started
  52         #   1 if daemon was already running
  53         #   2 if daemon could not be started
  54         start-stop-daemon --start --quiet --pidfile $PIDFILE --exec $DAEMON --test > /dev/null \
  55                 || return 1
  56         start-stop-daemon --start --quiet --pidfile $PIDFILE --exec $DAEMON -- \
  57                 $DAEMON_ARGS \
  58                 || return 2
  59         # Add code here, if necessary, that waits for the process to be ready
  60         # to handle requests from services started subsequently which depend
  61         # on this one.  As a last resort, sleep for some time.
  62 }
  63
  64 #
  65 # Function that stops the daemon/service
  66 #
  67 do_stop()
  68 {
  69         # Return
  70         #   0 if daemon has been stopped
  71         #   1 if daemon was already stopped
  72         #   2 if daemon could not be stopped
  73         #   other if a failure occurred
  74         start-stop-daemon --stop --quiet --retry=TERM/30/KILL/5 --pidfile $PIDFILE --name $NAME
  75         RETVAL="$?"
  76         [ "$RETVAL" = 2 ] && return 2
  77         # Wait for children to finish too if this is a daemon that forks
  78         # and if the daemon is only ever run from this initscript.
  79         # If the above conditions are not satisfied then add some other code
  80         # that waits for the process to drop all resources that could be
  81         # needed by services started subsequently.  A last resort is to
  82         # sleep for some time.
  83         start-stop-daemon --stop --quiet --oknodo --retry=0/30/KILL/5 --exec $DAEMON
  84         [ "$?" = 2 ] && return 2
  85         # Many daemons don't delete their pidfiles when they exit.
  86         rm -f $PIDFILE
  87         return "$RETVAL"
  88 }
  89
  90 #
  91 # Function that sends a SIGHUP to the daemon/service
  92 #
  93 do_reload() {
  94         #
  95         # If the daemon can reload its configuration without
  96         # restarting (for example, when it is sent a SIGHUP),
  97         # then implement that here.
  98         #
  99         start-stop-daemon --stop --signal 1 --quiet --pidfile $PIDFILE --name $NAME
 100         return 0
 101 }
 102
 103 SCRIPTNAME=$1
 104 scriptbasename="$(basename $1)"
 105 echo "SN: $scriptbasename"
 106 if [ "$scriptbasename" != "init-d-library" ] ; then
 107     script="$1"
 108     shift
 109     . $script
 110 else
 111     exit 0
 112 fi
 113
 114 NAME=$(basename $DAEMON)
 115 PIDFILE=/var/run/$NAME.pid
 116
 117 # Exit if the package is not installed
 118 #[ -x "$DAEMON" ] || exit 0
 119
 120 # Read configuration variable file if it is present
 121 [ -r /etc/default/$NAME ] && . /etc/default/$NAME
 122
 123 # Load the VERBOSE setting and other rcS variables
 124 . /lib/init/vars.sh
 125
 126 case "$1" in
 127   start)
 128         [ "$VERBOSE" != no ] && log_daemon_msg "Starting $DESC" "$NAME"
 129         do_start
 130         case "$?" in
 131                 0|1) [ "$VERBOSE" != no ] && log_end_msg 0 ;;
 132                 2) [ "$VERBOSE" != no ] && log_end_msg 1 ;;
 133         esac
 134         ;;
 135   stop)
 136         [ "$VERBOSE" != no ] && log_daemon_msg "Stopping $DESC" "$NAME"
 137         do_stop
 138         case "$?" in
 139                 0|1) [ "$VERBOSE" != no ] && log_end_msg 0 ;;
 140                 2) [ "$VERBOSE" != no ] && log_end_msg 1 ;;
 141         esac
 142         ;;
 143   status)
 144         status_of_proc "$DAEMON" "$NAME" && exit 0 || exit $?
 145         ;;
 146   #reload|force-reload)
 147         #
 148         # If do_reload() is not implemented then leave this commented out
 149         # and leave 'force-reload' as an alias for 'restart'.
 150         #
 151         #log_daemon_msg "Reloading $DESC" "$NAME"
 152         #do_reload
 153         #log_end_msg $?
 154         #;;
 155   restart|force-reload)
 156         #
 157         # If the "reload" option is implemented then remove the
 158         # 'force-reload' alias
 159         #
 160         log_daemon_msg "Restarting $DESC" "$NAME"
 161         do_stop
 162         case "$?" in
 163           0|1)
 164                 do_start
 165                 case "$?" in
 166                         0) log_end_msg 0 ;;
 167                         1) log_end_msg 1 ;; # Old process is still running
 168                         *) log_end_msg 1 ;; # Failed to start
 169                 esac
 170                 ;;
 171           *)
 172                 # Failed to stop
 173                 log_end_msg 1
 174                 ;;
 175         esac
 176         ;;
 177   *)
 178         echo "Usage: $SCRIPTNAME {start|stop|status|restart|force-reload}" >&2
 179         exit 3
 180         ;;
 181 esac
 182
 183 :
 184 </pre></p>
 185
 186 <p>It is based on /etc/init.d/skeleton, and could be improved quite a
 187 lot.  I did not really polish the approach, so it might not always
 188 work out of the box, but you get the idea.  I did not try very hard to
 189 optimize it nor make it more robust either.</p>
 190
 191 <p>A better argument for switching init system in Debian than reducing
 192 the size of init scripts (which is a good thing to do anyway), is to
 193 get boot system that is able to handle the kernel events sensibly and
 194 robustly, and do not depend on the boot to run sequentially.  The boot
 195 and the kernel have not behaved sequentially in years.</p>